CA2180111C

CA2180111C - A digital television system channel guide having a limited lifetime

Info

Publication number: CA2180111C
Application number: CA002180111A
Authority: CA
Inventors: John William Chaney
Original assignee: Thomson Consumer Electronics Inc
Current assignee: Technicolor USA Inc
Priority date: 1994-01-05
Filing date: 1995-01-04
Publication date: 2000-07-25
Anticipated expiration: 2015-01-04
Also published as: BR9506446A; CN100353759C; CA2479398A1; EP0738449B1; JPH09507361A; JP2013225902A; EP0838958B1; GB9400101D0; CA2479395A1; JP2005218130A; EP0838958A1; DE69508553T2; KR100385033B1; DE69508553D1; CA2479398C; WO1995019092A1; KR100336722B1; JP3962064B2; SG66236A1; FI114888B

Abstract

A television system for receiving a plurality of digitally-encoded television programs includes circuitry for selecting a particular digital data transmission channel from a plurality of digital data transmission channels containing a desired digitally-encoded television program in response to a control signal, at least one of the data transmission channels also including television program schedule data. The system also includes user-operable data entry circuitry for entering data, and a controller for generating the above-noted control signal in response to user-entered data. The controller selects a virtual channel from a plurality of virtual channels in response to user-entered data, each virtual channel being subject to reassignment to a different one of said a plurality of digital data transmission channels the television program schedule data defining the relationship of each of the television programs to respective ones of the plurality of digital data transmission channels.

Description

WO 9S119091 2 i 8 ~ .'C - -A DIGITAL TELEVISION SYSTEM CHANNEL GUIDE
HAVING A LIMITED LIFETIME
- FIF.T n OF T~F. INVENTION
This invention is related to the field of digital ~ ~ ons systems, and is described with reference to a digital satellite television system, but also may be ~~ ble to 10 such systems as a digital cable system, digital terrestrial broadcast system, or a digital c., ;~ ' ion system which utilizes telephone lines. The invention specifically concerns a method and apparatus for ensuring that the television schedule data, for generating screen displays for controlling the system, are current.
l S
BACKGROUNn OF W. INVF.NTION
In a satellite television c~.. -~.. ;~l;~ system, the satellite receives a signal c~ci,c.~ti~g audio, video, or data information from an earth-based ~ lllilt~,l. The satellite 2 0 amplifies and rebroadcasts this signal to a plurality of receivers, located at the homes of c. ~, via ~ o,~ operating at specified r.~. s and having given bandwidths. Such a system inc~udes an uplink 1. - g portion (earth to satellite), an earth-orbiting satellite receiving and ll....-~ g unit, and a 2 5 downlink portion (satellite to earth) including a receiver located at the user's residence. The subject matter of the present invention is especially ~ with a downlink receiving unit designed for relatively easy use by the user.
The subject system is designed to utilize two satellites 3 0 within a few degrees of each other in g~ earth-orbit stationed at an altitude of 22,300 miles, ~ uAi.~h~ly over the state of TeAas. With this all.l..g., --l receivers located anywhere in the contiguous 48 states of the United States can receive signals from both satellites on the same receiving antenna 3 5 dish without having to }eposition the antenna dish. E~ach satellite transmits its signals with a lcs~ live polarization. Selecting a WO 95119091 1 i ~ 5'~ ~
2~1~011~

satellite for reception of its signals is accomplished at the receiving antenna by selecting those signals with the appropriate S polarization. Each satellite includes sixteen transponders for L~ ..g signals to the receiving antenna dish over a range of rl.~ :~5. Each ~ iS time-multiplexed to convey a plurality of television channels (e.g., six to eight channels), subst~nti Illy simultaneously. The satellite signals are transmitted 10 in cv...~,..sse~ and p~ ;;7' d form, and comprise television and ancillary data signals. Because the system is capable of carrying as many as two hundred fifty-six channels, some television program selection method and apparatus, which is easy to , ' "~.d and operate, should be provided for the user.
If we look to c~ I analog VHF and UHF
broadcast television as a guide, we find that the solution provided therein is of little help, for the following reasons. The channel number of a given television station CVII~ '- to a fixed band of rl.,. - In other words, channel 6 in the United States is 2 0 regulated to occupy the range from 82-88 MHz. Most non-technical consumers have no und~,l ' g of the f ~ ,.l.,y ~lloc~ nc of the television broadcast bands. Instead, they tune a desired channel by entering its channel number into their receiver. Their receiver is ~,lv6l -~ with the proper 2 5 information to perform the required tuning to the desired channel by generating the appropriate bandswitching and tuning cc---- ' in response to the entering of the channel number by the user. It is possible for, ' c.~ to build a fixed channel number-to-frequency translation arrangement into each 3 0 television receiver, only because the relationship between channel number and rl.4_ y band must conform to a broadcast standard .
In the United States, there is a terrestrial television schedule guide system known as Starsight3 which provides a 3 5 channel guide display for selecting television channels at fixed broadcast frequencies. Starsight~8) data is 1..,..~...;l~. ~ in the ~ WO 9S/19091 218 ~ r~

vertical interYal of televisions programs of certain broadcasters (usually public broadcasting stations (PBS)), and displayed in the 5 form of a schedule guide on the user's television screen.
Unfortunately, three problems with the Starsight(~ system are perceived. First, it can take several hours for a Starsight~9 receiver to load its channel guide data due to its ~ n at a low data rate. Thus, a viewer will not be able to use his 10 Starsight3 system to tune channels for at least several hours after installing it in his home. Second, the channel guide infor~nation is not lldl.i,ll~ill~d on every channel, so updating the guide requires retuning to the PBS channel, thereby illt~,..ul,lillg the viewer's use of the receiver during the several hours it takes to reload the 15 guide. Third, a Starsight( D user must choose a several-hour window in time, which occurs once every twenty-four hours, for the Starsight(~' receiver to download a current copy of the channel guide. It is important to note that, . -Ypçct~d changes in the television schedule cannot be detected by the Starsight~ unit if 2 O the currently watched channel does not carry Starsight~ signals, and most channels do not carry those signals. Thus"",~r~,- d changes in the television schedule cannot be handled within a reasonable time due to, failure of the system to detect those changes, and the constraint of loading the schedule from a 2 5 particular broadcast station during a ~l~d~t~ .;lled time window.
SUMMARY OF T~F~ rNVF.l~TlON
A television system for receiving a plurality of digitally-encoded television programs includes an integrated 3 O receiver decoder (IRD) having circuitry for selecting a particular digital data llall~ -iSSiOn channel from a plurality of digital data transmission channels containing a desired digitally-encoded television program in response to a control signal, many of said data transmission channels also including television program 3 ~ schedule data. The system also includes user-operable data entry circuitry for entering data, and a controller for generating the WO 95/19091 2, ~.8 0 ~
above-noted control signal in response to user-entered data. The controller selects a virtual channel from a plurality of virtual 5 channels in response to user-entered data, each virtual channel being subject to re iCcign-- to a different one of said plurality of digital data trPnCmiCci~ channels, the television program schedule data defining the relationship of each of the television programs to us~,~.liv~ ones of the plurality of digital data 10 ~. ccion channels. The television schedule data being repeated several times per minute, and bearing a code indicative of its usable lifetime. The receiver acquires a new master program guide upon determining that its current channel guide has expired. In order to ~c~ .,û~-lr ~ d changes in 15 schedule, every few minutes the receiver checks a status byte to see if the master program guide has changed. The e~act number of minutes being ~ ,.u. -d to be several times less than the lifetime of the program guide. If the status byte indicates that the program guide has changed, then a new program guide is read in, 2 0 without waiting for the current guide to expire. The status byte may be a version number for the master program guide, which is compared to the version number of the currently-stored master program guide.
2 5 BRIFF DESCE2~PrlON OF THEI DRAWING
FIGURES I and 2 are illustrations of a typical l~
data stream from a lldl.SlJ J in accu.l' -- with the invention.
FIGURE 3 is an illustration of a program guide screen display 3 0 in accu.Ja.l~e with the invention.
FIGURE 4 is an illuslration of S~g~nt~tion of the master program guide and special program guides in accordance with the invention.
FTGURES 5a and 5b are illustrations of program data 3 5 structures in accordance with the invention.

WO 95/19091 2 1 8 0 1 1 ~ p~ l"~ C ~

FIGURE 6 is a block diagram of a satellite Il a~..... illg/receiving system according to the invention.
S FIGURE 7 is a block diagram of the IRD receiver unit.
FlGuRE 8 is a block diagram of a portion of the IRD receiver unit of FIGURES 6 and 7, in detdil.
FlGuRE 9 is a flow chart showing a portion of the control program of the l..i~. uc~ , . of the IRD receiver unit.
DETAlT Fn DF..~CRTPl'ION OF Tf lF. DRAWING
In the subject system, the information necessary to select a given television program is not fixedly-,uloE,Ia~...ed into each receiver but is rather is down-loaded from the satellite I S c.~ _-lly on each llal~S,u~C' . The television program selection information comprises a set of data known as a Master Program Guide (MPG), which relates television program titles, their start and end times, a virtual channel number to be displayed to the user, and information allocatin~ virtual channels to transponder 2 0 r~ h,s and to a position in the time- ltirl~ypd data stream llal-~ ,d by the particular llall~u~ 7 . In a system according to the subject invention, it is not possible to tune any channel until the first master program guide is received from the satellite, because the receiver literally does not know where any channel is located, in terms of rl~ ~ and position (i.e. data time slot) within the data stream of any llal~ r~ . Advantageously, the system is totally flexible in that any program may be assigned, or reassigned at any master program guide trancmiccil time, to any llal.i,poll~ or data time slot, in a fashion which is completely 3 0 lldlli~,ual~llt to the user, who sees only the I ' ~ ~ program title and virtual channel.
The problem of changes in television cchedule is overcome in that a master program guide prefer}-ably is transmitted on all l~al~ 7rs with television program video, 3 S audio, and auxiliary data, and is repeated periodically, for example, every 2 seconds. However, a system in which only one WO 95/19091 ^ P. ~

or some of the transponders catries the master program guide is also envisioned, in that a fast tuner could be employed to switch 5 to thc transponder carrying the master program guide, or a second tuner could be tuned to receive the master program guide data. The data rate for 11 g a master program guide is ~.u,.;...dtely 100 kbits per second. The master program guide, once received, is ...~ in a memory unit in the receiver, and updated periodically, for example every 30 minutes. Retention of the master program guide allows inctAntAnPollc television program se~ection because the necessary selection data are always available.
The master program guide has a lifetime (time within which its data is considered valid) of thirty minutes. A byte " ~ the remaining lifetime of the master program guide is l.A~ ,d with every IlA,. .";c~ n of the guide itself (i.e., about every two seconds). In addition to the thirty minute lifetime of a master program guide, an ~ guide" is available for 2 0 providing a way to correct errors in the program guide, caused by operator error at the uplink site, or caused by a sporting event running "overtime" (i.e., beyond its schcduled time). A program guide status byte (i.e., the "change number" byte) is checked repeatedly at the end of every five minute interval to see if the 2 5 content of the master program guide just received (but not yet stored) is changed from the content of the currently-stored master program guide. If so, then the newly-received master program guide is loaded into memory for immPrliAtP. use. If not, the newly-received master program guide is discarded.
3 0 Following is an explanation of how such a system is r lt ~ ~ 1 As noted above, the system is capable of IIAI.'...;IIi..g hundreds of programs. Each program may include a number of services. A service is defined herein as a program . such as a video signal, an audio signal, a closed caption 3 5 signal, or other data, including executable computer programs for an appropriate receiver. Each service of each program is WO95/19091 2 1 8 ~ }~J~ ,CC

identified by a unique Service Component Identifier (SCID). The information for the ~ y~Live services is Ll~n ~l--iLLcd in packets S of ~ t~ amounts of data (e.g., 130 bytes) and each packet includes an SCID cr,..c r " ~ to the service.
A ~ n of a typical data stream from one of the Llal. r ' is shown in FIGURE 1, and a typical packet from that data stream is shown in FIGURE 2. In FIGURE 1, a string of 10 boxes c~ ,s~..L~ signal pacl~ets which are , - of a plurality of different television progrâms Lla~ls~ by a given transponder. Packets with letters having like subscripts represent CGIllpull~--lo of a single television program. For example, packet identified as V1, Al and Dl, represent video, audio, and data for 15 program 1. In the upper line of the string of packets, the ;~ ,Cli~, CGlllp~ ts of a particular program are shown grouped together. However, it is not necessary to group CUI~p~ of a particular program together, as indicated by the packet sequence in the middle of the string. Moreover, there is no IC Illi~l..l..~..~l to 2 0 place the packets of a string in any particular order.
The string of packets shown in the lower portion of FIGURE 1, .~,.c;,~ three time multiplexed programs, programs 1, 2, and 3, plus packets ..,t,.~ ..ti.~g a program guide (packets D4). It is important to note that the data of the program guide 2 5 interrelates program co...p~ and virtual channels by virtue of the SCID. The .~,OJJ~Li~ packets are arranged to include a prefix and a payload as shown in FIGURE 2. The prefix of this example includes two 8-bit bytes comprising five fields, four of which are 1-byte fields (P,BB,CF,CS), and one 12-bit field (SCID).
3 0 The Payload portion contains the actual information to be received and processed. The exemplâry prefix includes a 1-bit priority field (P); a 1-bit boundâry field (BB), which indicates bu ' between gi~nifir~n~ signal chânges; a 1-bit field (CF), which indicates whether or not the payload is scrambled; a 1-bit field 3 5 (CS), which indicates which one of t~vo descrambling keys is to be used to descramble a s~ blcd payload; and a 12-bit SCID. The WO95fl9091 ~ r~/u.. ~

.~,...ail.d~,. of the packet Co...~ s the payload which may include error code parity bits appended to the end of the payload data.
A master program guide comprises packetized data formatted as defined above, and is assigned a specific SCID, such as, 0000 0000 0001. A master program guide comprises four sequential blocks of data, d~ci~rqt~, SEGM, APGD, CSSMI . . .
CSSMnseg, and PISMI . . . PlSMnseg, to be described below.
A master program guide typically includes television schedules for the next two hours, but may include schedules for four, six, or eight hours d~ on the size of the memory allocated to store it in the receiver. In addition to the master program guide, there is also provided one or more special program guides (SPG), cnntqining additional data, such as, for example, television program schedules for the following eight hours. That is, the master guide holds all information necessary for selecting current television programs, and the special guides contain information about future television programs. Special 2 0 guides are downloaded from the satellite as needed and are not retained in memory due to their large size. As shown in FIGURE 4, both the master program guide and special program guides are p~ iul~cd into a plurality of segments or portions (from 0 to 15) with an index "nseg" " ~ the current number of segments 2 5 comprising the special guide. Each segment carries program information for one or more virtual channels which range from 100 to 99g. FIGURE 4 shows OQly an exemplary allocation of virtual channels to segments, and other groupings can be, and are, made at the discretion of the operators at the satellite uplink 3 0 center. Each special guide segment includes two sequential blocks of data, CSSMI . . . CssMnce~ and PISMI . . . PlSMnseg, also to be described below.
FIGURES 5a and Sb illustrate program data structures of the subject system, not all of which are relevant to the virtual 3 5 channel selection and updating of the master program guide. Only those portion which are relevant will be fiiscucc~l Referring to SUBSI ~TUrE S~IEET (RULE 26) ~ WO 95119091 2 1 8 0 1 1 1 r~ ., . L . ~, t FIGURES 5a and Sb, the ~cment Map (SEGM) block of the master program guide contains information about the partitioning of the 5 channel space into segments, and the number of segments. The Additional Program uide I~ata (APGD) block contains a program guide map which indicates which special program guide segments are active, and their location (i.e., the particular transponder carrying the segment), as well as the SCIDs of the respective 10 segments. The APGD block contains program information relating to ratings and theme of a particular television program. The APGD
also includes a program guide map aCsoci~tin~ special guide segments with l~;.,U~ iV~ virtual channel names, virtual channel numbers, and content types.
The master guide and every special guide contain a Channel to ~ervice Segment Map (CSSM) block and a Program Information ~iegment Map (PISM) block. The CSSM describes virtual channels by defining characteristics such as, channel name, call letters, channel number, and type, which are in the 20 CU~ J ' Ig segment. The PISM block contains linked lists of program information such as, title, start time, duratiûn, rating, and category, that are on each virtual channel described in the r- ' ~ CSSM
Relevant portions of the data structures shown in 25 FIGURES 3, 4, Sa and Sb will be referred to in the following description of the program selection process. In order to understand the illlpUI L~ e of g an accurate master program guide, it may be helpful to describe how a master program guide is used to select a television program. Referring to 3 0 FIGURE 3, a user selects a television program for viewing, by moving a cursor (via operation of remote control up, down, ~ight, and left, direction control keys) to a block of the program guide screen display which contains the name of the desired program.
The remote control unit is not shown for simplicity. When a 3 5 SELECT key of the remote control is pressed, the current x and y WO 95119091 1 ~11~1..,5.'0~ , 2~8~
I o position of the cursor is evaluated to derive virtual channel and program time information.
S As shown in FIGURE 4, and as noted above, the master program guide and special program guides are divided into segments (which may be as little as one segment or as many as 16). The lowest vinual channel (100) is always allocated as the first channel of seg (0). Each segment contains channel and program information for a defined number of virtual channels.
Upon deriving the virtual channel number from the X and Y
cursor position information, the virtual channel number is used to point into the proper segment of the particular program guide (either master program guide, or a special program guide) to retrieve the specific channel information and program information. Specifically, the Channel Information (CI) Records in the CSSM (Channel to Service Segment Map) are a fixed length of seventeen bytes and contain such items as, the number of SClDs in use (typically 2, audio and video), the channel lla~ r (Chan 2 0 Xpndr) the channel number and short name (i.e., typically 4 Cll~ ,.t~.~), and a pointer into the linked program information. In order to access any specific Channel Information (Cl) it is only required to repeatedly add 17 to a base value. Program information includes the stan day and time of the program, the 2 5 number of 30 minute slots it occupies, the theme category (i.e., drama, sports, comedy), and parental rating.
Once the channel llal~sl~vl~dci carrying a desired television program is tuned, the data packets containing the audio and video information for that program can be selected from the 3 0 data stream received from the 11~ ' by ~Y:Iminin~ the data packets for the proper SCID (Service Component Identifier) 12 bit code. If the SCID of the currently received data packet matches the SCID of the desired television program as listed in the program guide, then the data packet is routed to the proper data 35 processing sections of the receiver, if the SCID of a panicular 218~
packet does not match the SCID of the desired television program as listed in the program guide, then that data packet is discarded.
Referring again to the Segment Map (SEGM), of FIGURE
Sa, there are included in the SEGM two bytes of particular interest. The first is the lifetime byte which is initially set to thirty minutes when a new master program guide is first ~Id~ ed. Each tran~rniCc;on of that same master program 10 guide will have the lifetime byte de~ e~lt-,~ by an amount equal to the time delay between tr~nc~niCci~ ~ of that guide (typically, every two seconds). When the lifetime byte reaches a value of zero (in~iirl~-ing that the currently stored master program guide is thirty minutes old), then a new master program guide is acquired and stored for ;"",.rJh,t, use. The second byte of particular interest is the "change number" byte. Each master program guide having content which is different from the content of the currently-stored master program guide will have a different number from the currently-stored master program guide. It is this byte which will be examined to determine whether an I s~ d change in p-u~,-allllllillg has occurred (i.e., a change in television ~lu~ lllllling which occurred during the valid lifetime of the currently-stored master program guide).
Detection of such an ~ change requires the acquisition and storage of a new master program guide. At the end of every five minute interval (although another time period may be used) during the valid lifetime of the currently-stored master program guide, the "change number" byte of a newly received guide will be examined to d~,L.,I, ~ if a change in master program guide 3 0 content has occurred, and whether or not the newly-received master program guide should be stored and used, or discarded.
The "change number" byte may be a version number for the master program guide, which is compared tO the version number of the currently-stored master program guide. A flowchart 3 5 illustrating the portion of the control program for the receiver WO 95/19091 ~,g which is relevant to the master program guide updating operation is shown in FIGURE 9.
The routine of FIGURE 9 is entered at step 900 and proceeds to step 910 wherein a check is made to see if the lifetime of thirty minutes of the currently-stored master program guide has expired. If so, the program advances to step 920 to acquire and store a new master program guide, and then exits at step 990. If, at step 910, the lifetime of the currently-stored master program guide had not expired, then the NO path is taken to step 930 wherein a check is made to see if five minutes has elapsed since the last time that change number byte was ~'Y -' If the five minute period has not elapsed, then the I S routine is exited at step 990. If the five minute period has elapsed, then the change number byte is read at step 940. At step 950, a d~t~ ...;,.~ion is made as to whether or not the newly-received master program guide has been changed from the currently-stored master program guide. If so, the program 2 0 advances to step 920 to acquire and store a new master program guide, and then exits at step 990. If not, then the NO path is taken to the exit at step 990. Thus, in the normal course of events, every thirty minutes the master program guide is updated with new information. However, in the event of an, - . : :i 2 S television program schedule change, the receiver will correct its master program guide within a five minute period, because a master program guide including schedule data for all active virtual channels is L.~...al..ilt~d on every lldl~ isaion channel every two seconds, and because a complete new master program 3 0 guide takes only two seconds to load.
A brief description of system hardware, suitable for implementing the above-described invention, now follows. In FIGURE 6, a L.~ t~,. 601 processes a data signal from a source 614 (e.g., a television signal source) and transmits it to a satellite 3 5 613 which receives and rebroadcasts the signal to a receiver 612.
Tlallalll;llt;l 601 includes an encoder 602, a mod~ tor/forward -WO 95~19091 ~ P~

error corrector (FEC) 603, and an uplink unit 604. Encoder 602 ~;~...~,.,,~ses and encodes signals from source 614 according to a 5 ~ t~ ed standard such as MPEG. MPEG is an int~mqti~ -standard developed by the Moving Picture Expert Group of the Int~,.,dti~ Standards Orgs~i7q~ for coded l~ ,scl~Lation of moving pictures and qccociqt- d audio stored on digital storage medium. An encoded signal from unit 602 is supplied to 10 mod~lq~or/Forward Error Corrector (FEC) 603, which encodes the signal with error correction data, and Q. Ildly Phase Shift Key (QPSK) modlliqr~s the encoded signal onto a carrier. Both convolutional and Reed-Solomon (RS) block coding are performed in block 603.
Uplink unit 604 transmits the co.. ~l~s~cd and encoded signal to satellite 613, which broadcasts the signal to a selected 6c~,-d~hic reception area. In this c...bodi...~,At, satellite 613 operates in two modes, which trade off channel capacity for trqr~emicei~n power, or transmission power for channel capacity.
2 0 In the first mode, satellite 613 illustratively transmits sixteen channels at 120 watts each. In the second mode, satellite 613 transmits eight channels at 240 watts each.
The signal from satellite 613 iS received by an antenna dish 605 coupled to an input of a so-called set-top receiver 612 2 5 (i.e., an interface device situaled atop a television receiver).
Receiver 612 includes a d ~ qtr~r/Forward Error Correction (FEC) decoder 607 to ~i~moril-~ the signal and to decode the error correction data, a mi~.u~ ssu. 606, which operates illt~ld~ ly with d~mod~llq~rlrlFEc unit 607, and a transport unit 3 0 608 to transport the signal to an d~ Jl;dl~ decoder within unit 609 ~ r ~ing on the content of the signal, i.e., audio or video information. Transport unit 608 receives corrected data packets from unit 607 and checks the header of each packet to detemmine its routing. Decoders in unit 609 decode the signal and remove 35 added transport data, if used. An NTSC Encoder 610 encodes the WO 95/19091 2 i8 0 1 ~
decoded signal to a format suitable for use by signal processing circuits in a standard NTSC consumer television receiver 611.
FIGURE 7 is a block diagram showing the components of tho IRD receiver system including the outdoor antenna dish unit 7-5. The IRD includes a block 707 including a tuner 734 and a d~oA~ tor unit 735 for tuning various television signals. The IRD is under control of a .lli~.u..u.llluller 706, which also controls the interfaces between the IRD and a telephone network via a telephone modem 734, between the IRD and a user via an IR link 725 and between the IRD and a television receiver via an MPEG
decoder 723, a video encoder 721, and an RF modulator 722, and finally, between the IRD unit and a user via a smart card interface and transport IC 708. The masoer program guide is stored, for example, in RAM 709.
Referring now to FIGURE 8, d~mod--lqtnrtFEC unit 807 acquires, ~mod~ s, and decodes the data signal which is received from antenna dish 805. This unit includes a tuner 834, a 2 0 Quaternary Phase Shift Key (QPSK) ~ (llllqtl~r 835, a Viterbi convolutional decoder 836, a de-interleaver 837, and a Reed-Solomon (RS) decoder 838, all of conventional design, arranged as shown .
Tuner 834 receives an input signal from antenna dish 805. Based upon a user's channel selection, a control unit 806 (i.e., a l..h,.u~,.ucessul) sends a r..~ y signal to tuner 834. This signal cause tuner 834 to tune to the appropriate channel and to do~ the received signal in rl~ . y in response to the tuning frequency signal sent to tuner 834 from lllh,lu~Jlùcc~su 3 0 806. An output signal from tuner 34 is provided to QPSK
demodulator 835.
QPSK t~mo~ tor 835 locks onto (~yllC}IlulliZ.,S with) the tuned channel, d~mo~l.-l~t.~s the modlll~tl~d data signal, and generates a signal indicative of the quality of the d~modlll1lt~d 3 5 signal. D~modlll~tor 835 d~mod~ t~s the mûdlll~tl-d input data signal regardless of the error correction code rate of the received W095/19091 ~18~ P~ J..,.),'C~
data signal. Phase-locked loop circuitry in demo~ll-lqtor 835 ~y ', ~ Ihe operation of demodulator 835 with the input 5 signal using well-known techniques. Demodulator 835 generates a Demodulator Lock output eontrol signal that indicates whether or not l~mod~ r 835 is ~ ' ,c 7~d with the input signal, and supplies this signal to a storage register in mi~lv~.ùcc;,sor 806.
an output ~modlllqt~d data signal from unit 835 is provided to 10 Viterbi decoder 836. Dl ~ ' 835 also generates an output Signal Quality signal, which is indicative of the quality of the signal received from the satellite transmission, and is related to the signal-to-noise ratio of the received signal. Various sources of noise, as well as rain fade, may impair the quality of a received 15 signal. A QPSK ho.ll ~ . suitable for use as unit 835 is eommercially available from Hughes Network Systems of G~,lllldilLuwll, Maryland (illt~,~;làt~d circuit type No. 1016212), and from Comstream Corp.,. San Diego California (No. CD2000).
Decoder 836 uses a Viterbi algorithm to decode and to 2 0 correct bit errors in the d~Pmf ' lq~Pd signal from unit 835.
Decoder 836 includes internal networks, as known, to ~yll~,lllo its operation to the incoming ' -' Iqt.-d signal in order to effectively decode the f' _' lq-~d signal.
After decoder 836 decodes and error corrects the 2 5 d~ d IqtPd data signal, the decoded data signal is supplied to a de-interleaver 837. De-int~,.lca~ 837 restores the ordering of the data signal to its original sequence, and forms Reed-Solomon blocks (RS blocks), in accu,~' with known t~P~hni~,_ . For this purpose de-interleaver 837 relies upon an 8-bit sync word inserted by the encoder at the beginning of each RS block, thereby providing RS block ~yll~ lu~ aliOn. The de-illt~rlcàvc~ signal is supplied to a Reed-Solomon (RS) decoder 838.
RS decoder 838 decodes the RS blocks and corrects byte errors within a block. A decoded signal from Viterbi decoder 3 5 836 is provided to RS decoder 838 via de-interleaver 837. If decoder 36 uses the proper error correction decode rate to decode the data signal, de-interleaver 837 and Reed-Solomon decoder 838 will operate normally.
Thus, a digital multi-channel transmission system has been disclosed and described which allocates television programs to ~ ers and to time- ' . '-Y~d slots in the data stream of a given transponder in a way which is completely ~IdllSl10.lC;llt to the user, who simply tunes a desired television program by selecting a virtual channel. Clearly, the key to smooth operation of this system is the l~A~ ;on of the master and special channel guides which relate lldll:~l.l- '1- channels and program data positions in the LlA~ ond~ data stream to virtual channel numbers. The subject invention ensures that the stored master program guide data are current by reloading it every half hour, and by checking every five minutes to see if the content of a newly-received master program guide differs from the content of the currently-stored master program guide.

Claims

1. A television system for receiving a plurality of digitally-encoded television programs wherein each of said digitally-encoded television programs is associated with at least one of a plurality of digital data transmission channels, each of said digital data transmission channels has the capacity to transmit at least one digitally-encoded television program and at least one of said plurality of digital data transmission channels includes television program schedule data, said system comprising:
means responsive to a control signal for selecting a particular digital data transmission channel from said plurality of digital data transmission channels; and control means coupled to said selecting means for generating said control signal;
said television program schedule data being updated at predetermined time intervals and comprising:
a first data structure defining the relationship of each of said television programs to respective ones of said plurality of digital data transmission channels, a second data structure indicative of a time period during which said defined relationships are valid, and a third data structure indicative of a change in said defined relationships;
said control means causing said first data structure of said television program schedule data to be acquired and stored when said second data structure indicates that said valid time period is less than a predetermined time period or when said third data structure indicates that said defined relationships have changed;
said control means examining said third data structure more often than said second data structure.

2. The television system of claim 1 wherein each of said digital data transmission channels includes said television program schedule data.

3. The television system of claim 1 wherein said time period of said second data structure is of the order of thirty minutes.

4. The television system of claim 1 wherein said third data structure comprises information indicative of a version of said television program schedule data.

5. A method for receiving a plurality of digitally-encoded television programs wherein each of said digitally-encoded television programs is associated with at least one of a plurality of digital data transmission channels, each of said digital data transmission channels has the capacity to transmit at least one digitally-encoded television program and at least one of said plurality of digital data transmission channels includes television program schedule data, said method comprising:
selecting a digital data transmission channel including television program schedule data from said plurality of digital data transmission channels, said television program schedule data being updated at predetermined time intervals and comprising:
a first data structure defining the relationship of each of said television programs to respective ones of said plurality of digital data transmission channels, a second data structure indicative of a time period during which said defined relationships are valid, and a third data structure indicative of a change in said defined relationships;
examining said second and third data structures of said television program schedule data of said selected digital data transmission channel, said third data structure being examined more frequently than said second data structure;
acquiring and storing said first data structure of said television program schedule data of said selected digital data transmission channel if said examination of said second data structure indicates that said valid time period is less than a predetermined time period or if said examination of said third data structure indicates that said defined relationships have changed.

6. The method of claim 5 wherein each of said digital data transmission channels includes said television program schedule data.